1. Field of the Invention
The present invention relates to the field of fabricating a semiconductor device and, more particularly, to methods for fabricating a semiconductor device having slopes at lower sides of an interconnection hole with an etch-stop layer.
2. Description of the Related Art
In general, in high-performance, highly integrated semiconductor devices, upper and lower metal layers are connected using a multi-layered structure. Al (aluminum), which is used as the metal wiring in a conventional process of fabricating the semiconductor device, is not suitable for fabricating the highly integrated semiconductor devices due to problems such as electromigration, low melting point and the like. Thus, a metal such as copper is used instead, which has relatively better electromigration characteristic, lower resistance, and a higher melting point than Al.
The metal wirings of the multi-layered structure are interconnected by a via hole, and it is very important to form a metal layer without a void occurring within the via hole of the highly integrated semiconductor device having a high aspect ratio. The metal layer may be formed by using physical vapor deposition, chemical vapor deposition, or electrochemical deposition and the like. However, in accordance with characteristics of each metal, the method for forming a metal layer is limited. For example, when the physical vapor deposition method is used to form a copper layer, characteristics of step coverage deteriorate. As a result, an overhang is formed at an entrance of the via hole or a contact hole, which is to be filled with the copper layer. When the chemical vapor deposition method is used to form a copper layer, there is the weak point that nonvolatile solid state CuCl2 is generated during the deposition process.
The above-mentioned problems can be overcome by an electrochemical deposition method. The U.S. Pat. No. 5,256,274 to Poris et al discloses a method for forming the copper layer by using the electrochemical deposition method, entitled “Selective Metal Electrodeposition”.
Hereinafter, the method for fabricating the conventional metal wirings using the electrochemical deposition method will be described with reference to FIGS. 1A to 1F, FIGS. 2A and 2B, and FIG. 3.
Referring to FIG. 1A, on a semiconductor substrate 10 including a completed lower structure consisting of a device isolation layer 11, a gate electrode 12 and an insulating spacer 13, an etch-stop layer 14 and an interlayer dielectric layer 15, which are consecutively formed.
Referring to FIG. 1B, at least one preliminary via hole 15a for exposing the etch-stop layer 14 within the interlayer dielectric layer 15 is formed by selectively etching the interlayer dielectric layer 15.
Referring to FIG. 1C, a via hole 15b for exposing the gate electrode 12 is formed by removing the exposed etch-stop layer 14 at the bottom surface of the preliminary via hole 15a. 
Referring to FIG. 1D, the interlayer dielectric layer 15 including the via hole 15b and the exposed gate electrode 12 are covered with a seed layer 16 by a physical vapor deposition method. The seed layer 16 is connected to an electrode in a subsequent electrochemical deposition process. A metal diffusion barrier layer may be formed before forming the seed layer 16.
As can be seen from the FIG. 1E, by forming a metal layer 17 such as copper layer on the seed layer 16 by the electrochemical deposition method, the via hole 15b is filled with the metal layer 17.
Next, as can be seen from the FIG. 1F, a CMP (chemical mechanical polishing) process allows the seed layer 16 and the metal layer 17 to remain behind within the via hole 15b so that a seed layer pattern 16a and a metal layer pattern 17a are formed.
FIGS. 2A and 2B show partially enlarged views of the ‘A’ portion of FIG. 1D, and in particular show cases when the etch-stop layer 14 is removed by performing anisotropic etching and wet etching, respectively.
As can be seen from the FIG. 2A, when the etch-stop layer 14 is removed by the anisotropic etching process, the bottom surface of the via hole 15b has a vertical profile 30. As can be seen from the FIG. 2B, when the etch-stop layer 14 is removed by the wet etching process, the bottom surface of the via hole 15b may have an undercut profile 40. As such, step coverage of the seed layer 16 formed by the physical vapor deposition method is poor in both cases.
FIG. 3 shows a partially enlarged view of the ‘A’ portion of FIG. 1E, and in particular shows the case when the metal layer 17 is formed on the seed layer 16 with poor step coverage by the electrochemical deposition method. The via hole 15b is not completely filled with the metal layer 17, thereby a void 50 forms in a lower portion of the via hole 15b due to the poor step coverage of the seed layer 16. In addition, when the step coverage of the seed layer 16 is poor, the metal layer 17 formed by the electrochemical deposition method delaminates or comes off the bottom surface of the via hole. Furthermore, when the void 50 is generated, a residue of an electrolyte remains within the void 50. Thus, corrosion of the metal layer 17 due to the residual electrolyte may occur, or explosion of the metal layer 17 may occur due to a gas resulting from the liquid electrolyte during a subsequent thermal process.